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id="post-info"><h1 class="post-title">Vue源码开发-批量更新06</h1><div id="post-meta"><div class="meta-firstline"><span class="post-meta-date"><i class="far fa-calendar-alt fa-fw post-meta-icon"></i><span class="post-meta-label">发表于</span><time class="post-meta-date-created" datetime="2021-01-04T16:00:00.000Z" title="发表于 2021-01-05 00:00:00">2021-01-05</time><span class="post-meta-separator">|</span><i class="fas fa-history fa-fw post-meta-icon"></i><span class="post-meta-label">更新于</span><time class="post-meta-date-updated" datetime="2021-01-04T16:00:00.000Z" title="更新于 2021-01-05 00:00:00">2021-01-05</time></span><span class="post-meta-categories"><span class="post-meta-separator">|</span><i class="fas fa-inbox fa-fw post-meta-icon"></i><a class="post-meta-categories" href="/categories/%E6%BA%90%E7%A0%81/">源码</a></span></div><div class="meta-secondline"><span class="post-meta-separator">|</span><span class="post-meta-wordcount"><i class="far fa-file-word fa-fw post-meta-icon"></i><span class="post-meta-label">字数总计:</span><span class="word-count">2.9k</span><span class="post-meta-separator">|</span><i class="far fa-clock fa-fw post-meta-icon"></i><span class="post-meta-label">阅读时长:</span><span>11分钟</span></span><span class="post-meta-separator">|</span><span class="post-meta-pv-cv" id="" data-flag-title="Vue源码开发-批量更新06"><i class="far fa-eye fa-fw post-meta-icon"></i><span class="post-meta-label">阅读量:</span><span id="busuanzi_value_page_pv"></span></span></div></div></div></header><main class="layout" id="content-inner"><div id="post"><article class="post-content" id="article-container"><h1 id="Vue源码开发-批量更新"><a href="#Vue源码开发-批量更新" class="headerlink" title="Vue源码开发-批量更新"></a>Vue源码开发-批量更新</h1><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 我们前面已经知道了 每个属性都会对应一个dep实例 而每个dep实例都会有一个watcher 这个watcher 是渲染用的 </span><br><span class="line"><span class="number">2.</span> 而 watcher 实例里面 有模版 依赖的 data里面数据的变量 对应的dep实例</span><br><span class="line"><span class="number">3.</span> 当我们改变对应data里的数据 就会触发set函数 然后对应的变量的dep就会触发notify函数 从而调用watcher里面更新函数 也就是调用了_update函数 和 _render 函数 </span><br><span class="line"><span class="number">4.</span> 所以这我们改变了几个data的数据变量 就会调用几次watcher 这样是不合理的 </span><br><span class="line"><span class="number">5.</span> 这里我们要改用异步更新的方式去处理批量更新 如果多个data里的数据放生改变了 我们只更新一次</span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">&quot;app&quot;</span> <span class="attr">class</span>=<span class="string">&quot;init&quot;</span> <span class="attr">style</span>=<span class="string">&quot;color: red;height: 200px;&quot;</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">span</span>&gt;</span>&#123;&#123;product&#125;&#125;<span class="tag">&lt;/<span class="name">span</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">div</span>&gt;</span>你好<span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">div</span>&gt;</span>&#123;&#123;list&#125;&#125;<span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">&quot;./dist/umd/vue.js&quot;</span>&gt;</span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="javascript">        <span class="keyword">let</span> vm = <span class="keyword">new</span> Vue(&#123;</span></span><br><span class="line"><span class="javascript">            el:<span class="string">&#x27;#app&#x27;</span>,</span></span><br><span class="line"><span class="javascript">            data:<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span></span><br><span class="line"><span class="javascript">                <span class="keyword">return</span> &#123;</span></span><br><span class="line"><span class="javascript">                    product:<span class="string">&#x27;3;33&#x27;</span>,</span></span><br><span class="line"><span class="javascript">                    list:<span class="string">&#x27;333&#x27;</span>,</span></span><br><span class="line"><span class="javascript">                    name:<span class="string">&#x27;北城&#x27;</span></span></span><br><span class="line">                &#125;</span><br><span class="line">            &#125;,</span><br><span class="line">        &#125;)</span><br><span class="line"><span class="javascript">        <span class="built_in">setTimeout</span>(<span class="function">() =&gt;</span> &#123;</span></span><br><span class="line"><span class="javascript">            vm.product = <span class="string">&#x27;我改变了&#x27;</span></span></span><br><span class="line"><span class="javascript">            vm.list = <span class="string">&#x27;你好&#x27;</span></span></span><br><span class="line">        &#125;,1000)</span><br><span class="line">    <span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 我们上面可以看到 我们改变了 product 和 list 数据</span><br><span class="line"><span class="number">2.</span> 此时已经触发了两次watcher里的更新视图的方法 就会重复渲染</span><br><span class="line"><span class="number">3.</span> 这样是不合理的 因为我们只做一次渲染  所以我们要做批量更新 和 异步更新 也就是防抖</span><br></pre></td></tr></table></figure>
<p><img src="1.gif" alt=""></p>
<h2 id="异步更新-批量更新"><a href="#异步更新-批量更新" class="headerlink" title="异步更新 批量更新"></a>异步更新 批量更新</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 首先我们要明确 如果你多次改变data中的数据 我们更新视图的操作应该只执行一次</span><br><span class="line"><span class="number">2.</span> 另外我们的视图更新 应该是异步的形式 也就是说等你同步的操作都完毕了 我们才去更新视图</span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">&quot;app&quot;</span> <span class="attr">class</span>=<span class="string">&quot;init&quot;</span> <span class="attr">style</span>=<span class="string">&quot;color: red;height: 200px;&quot;</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">span</span>&gt;</span>&#123;&#123;product&#125;&#125;<span class="tag">&lt;/<span class="name">span</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">div</span>&gt;</span>你好<span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">div</span>&gt;</span>&#123;&#123;list&#125;&#125;<span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">&quot;./dist/umd/vue.js&quot;</span>&gt;</span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="javascript">        <span class="keyword">let</span> vm = <span class="keyword">new</span> Vue(&#123;</span></span><br><span class="line"><span class="javascript">            el:<span class="string">&#x27;#app&#x27;</span>,</span></span><br><span class="line"><span class="javascript">            data:<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span></span><br><span class="line"><span class="javascript">                <span class="keyword">return</span> &#123;</span></span><br><span class="line"><span class="javascript">                    product:<span class="string">&#x27;3;33&#x27;</span>,</span></span><br><span class="line"><span class="javascript">                    list:<span class="string">&#x27;333&#x27;</span>,</span></span><br><span class="line"><span class="javascript">                    name:<span class="string">&#x27;北城&#x27;</span></span></span><br><span class="line">                &#125;</span><br><span class="line">            &#125;,</span><br><span class="line">        &#125;)</span><br><span class="line"><span class="javascript">        <span class="comment">// 这里我们对data里的数据做了多次重复的操作 按照我们之前的代码 肯定改变一次就会调用一个渲染</span></span></span><br><span class="line"><span class="javascript">        <span class="comment">// 视图的方法 所以这样是不合理的 </span></span></span><br><span class="line"><span class="javascript">        <span class="comment">// 另外没改变一次数据 我们应该只取最后一次去改变</span></span></span><br><span class="line"><span class="javascript">        <span class="built_in">setTimeout</span>(<span class="function">() =&gt;</span> &#123;</span></span><br><span class="line"><span class="javascript">            vm.product = <span class="string">&#x27;我改变了&#x27;</span></span></span><br><span class="line"><span class="javascript">            vm.list = <span class="string">&#x27;你好&#x27;</span></span></span><br><span class="line"><span class="javascript">            vm.product = <span class="string">&#x27;要改变&#x27;</span></span></span><br><span class="line"><span class="javascript">            vm.list = <span class="string">&#x27;是的&#x27;</span></span></span><br><span class="line">        &#125;,1000)</span><br><span class="line">    <span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 这里我们知道 我们更新的时候 是调用watcher里的方法去更新 </span><br><span class="line"><span class="number">2.</span> 每个数据改变 就会调用对应的dep 然后dep去调用watcher中的更新方法 这些dep中的watcher有一些是相同的</span><br><span class="line"><span class="number">3.</span> 所以我们首先要去重 让拥有相同watcher的dep实例 只保留一个 watcher </span><br><span class="line"><span class="number">4.</span> 然后我们更新的时候 采用一个调度函数的方法去更新</span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> &#123; popTarget, pushTarget &#125; <span class="keyword">from</span> <span class="string">&quot;./dep&quot;</span></span><br><span class="line"><span class="keyword">import</span> &#123; queueWatcher &#125; <span class="keyword">from</span> <span class="string">&quot;./schedular&quot;</span></span><br><span class="line"><span class="keyword">let</span> count = <span class="number">0</span></span><br><span class="line"><span class="comment">//20201 02 17</span></span><br><span class="line"><span class="keyword">let</span> id = <span class="number">0</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Watcher</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="title">constructor</span>(<span class="params">vm,exprOrFn,cb,options</span>)</span>&#123;</span><br><span class="line">        <span class="built_in">this</span>.vm = vm</span><br><span class="line">        <span class="comment">//1. exprOrFn 就是我们传入进来的 updateComponent函数 这里面就是</span></span><br><span class="line">        <span class="comment">// _update _render 函数 调用之后就会更新页面</span></span><br><span class="line">        <span class="built_in">this</span>.getter = exprOrFn</span><br><span class="line">        <span class="built_in">this</span>.cb = cb</span><br><span class="line">        <span class="built_in">this</span>.options = options</span><br><span class="line">        <span class="built_in">this</span>.id = id++</span><br><span class="line">        <span class="built_in">this</span>.deps = []</span><br><span class="line">        <span class="built_in">this</span>.depsId = <span class="keyword">new</span> <span class="built_in">Set</span>()</span><br><span class="line">        <span class="comment">//2. 这里我们抽离一下 方便我们记录 模版都依赖了data中的哪些数据变量</span></span><br><span class="line">        <span class="built_in">this</span>.get()</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="title">get</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="comment">//4. 走到这里的时候 我们就把watcher放入到我们的dep上</span></span><br><span class="line">        pushTarget(<span class="built_in">this</span>)</span><br><span class="line">        <span class="comment">// 3. 这个方法 就会对我们的 data 中的数据进行取值 </span></span><br><span class="line">        <span class="comment">// 因为我们的data是被劫持过的 所以我们一取值 就会触发get函数</span></span><br><span class="line">        <span class="built_in">this</span>.getter()</span><br><span class="line">        <span class="comment">//5. 当页面更新之后 我们在把target 至为null</span></span><br><span class="line">        popTarget()</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">// 6.存放dep的方法 要去重 </span></span><br><span class="line">    <span class="comment">// 因为我们 会出现多个重复的依赖数据 而我们只需要用一个 所以要去重复</span></span><br><span class="line">    <span class="comment">//&lt;div&gt;&#123;&#123;product&#125;&#125;&lt;/div&gt; &lt;span&gt;&#123;&#123;product&#125;&#125;&lt;/span&gt;</span></span><br><span class="line">    <span class="comment">// 以上 我们由于编译成render函数之后 会去 data的数据上去值</span></span><br><span class="line">    <span class="comment">// 一取值 就会触发get函数 而这里 触发了两次get函数 但是数据是相同的</span></span><br><span class="line">    <span class="comment">// 所以要去重复</span></span><br><span class="line">    <span class="function"><span class="title">addDep</span>(<span class="params">dep</span>)</span>&#123;</span><br><span class="line">        <span class="keyword">let</span> id = dep.id</span><br><span class="line">        <span class="keyword">if</span>(!<span class="built_in">this</span>.depsId.has(id))&#123;</span><br><span class="line">            <span class="built_in">this</span>.depsId.add(id)</span><br><span class="line">            <span class="built_in">this</span>.deps.push(dep)</span><br><span class="line">            dep.addSub(<span class="built_in">this</span>)</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="title">update</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="comment">// console.log(&#x27;调用了watcher里面的方法&#x27;)</span></span><br><span class="line">        <span class="comment">// this.get()</span></span><br><span class="line">        <span class="comment">//2021 0218 这里我们知道我们如果多次数据发生改变 都会调用这个update方法</span></span><br><span class="line">        <span class="comment">// 而我们其实只需要调用一次更新视图的方法 所以这里我们要写一个调度的函数</span></span><br><span class="line">        <span class="comment">// 目的就是为了多次更新的时候我们只更新一次视图</span></span><br><span class="line">        queueWatcher(<span class="built_in">this</span>)</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">//4. 这个就是真正意义上的更新视图的方法 通过 调度函数 flushSchedularQueue 去做更新</span></span><br><span class="line">    <span class="function"><span class="title">run</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="built_in">this</span>.get()</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">default</span> Watcher</span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// observe / schedular.js</span></span><br><span class="line"></span><br><span class="line"><span class="comment">//  2021 0218 </span></span><br><span class="line"><span class="comment">//2. 这里的目的就是更新的时候 就多次去重</span></span><br><span class="line"><span class="comment">// 这里我们知道 每个劫持的数据对应的dep 当触发更新的时候 使用的都是同一个watcher </span></span><br><span class="line"><span class="comment">// 所以这里我们要去重</span></span><br><span class="line"><span class="keyword">let</span> has = &#123;&#125;</span><br><span class="line"><span class="keyword">let</span> queue = []</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">queueWatcher</span>(<span class="params">watcher</span>)</span>&#123;</span><br><span class="line">    <span class="comment">// 第一次has里是没有id的键的 所以会进入到判断条件里面</span></span><br><span class="line">    <span class="comment">// 在if里面 我们就把has[id]的值设置为true</span></span><br><span class="line">    <span class="comment">// 所以第二次的时候 就不会进入到if里 此时 queue只有一个watcher</span></span><br><span class="line">    <span class="keyword">let</span> id = watcher.id</span><br><span class="line">    <span class="keyword">if</span>(has[id] == <span class="literal">null</span>)&#123;</span><br><span class="line">        queue.push(watcher)</span><br><span class="line">        has[id] = <span class="literal">true</span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line">        <span class="comment">// 让queue清空 这里是异步完成的 </span></span><br><span class="line">        <span class="built_in">setTimeout</span>(flushSchedularQueue,<span class="number">0</span>)</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">//3. 这里主要就是做调度去使用 调度我们更新的函数 去做视图更新 执行完毕之后 清空我们的调度队列</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">flushSchedularQueue</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="comment">// watcher 会有多个 所以 我们要 循环</span></span><br><span class="line">    <span class="keyword">for</span>(<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; queue.length; i++)&#123;</span><br><span class="line">        <span class="keyword">let</span> watcher = queue[i]</span><br><span class="line">        watcher.run()</span><br><span class="line">    &#125;</span><br><span class="line">    queue = []</span><br><span class="line">    has = &#123;&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h2 id="存在问题"><a href="#存在问题" class="headerlink" title="存在问题"></a>存在问题</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 通过上面的代码 我们已经实现了异步更新</span><br><span class="line"><span class="number">2.</span> 但是有个问题 由于我们更新是 异步的 所以我们拿不到最新渲染之后的DOM元素</span><br><span class="line"><span class="number">3.</span> 这里需要注意的是 我们每次执行完_update 和 _render 函数之后 都把最新创建的DOM挂在到了 $options.el上</span><br><span class="line"><span class="number">4.</span> 所以我们可以通过实例的$options.el拿到更新后的DOM元素</span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">&quot;app&quot;</span> <span class="attr">class</span>=<span class="string">&quot;init&quot;</span> <span class="attr">style</span>=<span class="string">&quot;color: red;height: 200px;&quot;</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">span</span>&gt;</span>&#123;&#123;product&#125;&#125;<span class="tag">&lt;/<span class="name">span</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">div</span>&gt;</span>你好<span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">         <span class="tag">&lt;<span class="name">div</span>&gt;</span>&#123;&#123;list&#125;&#125;<span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">&quot;./dist/umd/vue.js&quot;</span>&gt;</span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="javascript">        <span class="keyword">let</span> vm = <span class="keyword">new</span> Vue(&#123;</span></span><br><span class="line"><span class="javascript">            el:<span class="string">&#x27;#app&#x27;</span>,</span></span><br><span class="line"><span class="javascript">            data:<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span></span><br><span class="line"><span class="javascript">                <span class="keyword">return</span> &#123;</span></span><br><span class="line"><span class="javascript">                    product:<span class="string">&#x27;3;33&#x27;</span>,</span></span><br><span class="line"><span class="javascript">                    list:<span class="string">&#x27;333&#x27;</span>,</span></span><br><span class="line"><span class="javascript">                    name:<span class="string">&#x27;北城&#x27;</span></span></span><br><span class="line">                &#125;</span><br><span class="line">            &#125;,</span><br><span class="line">            methods:&#123;&#125;</span><br><span class="line">        &#125;)</span><br><span class="line"><span class="javascript">        <span class="built_in">setTimeout</span>(<span class="function">() =&gt;</span> &#123;</span></span><br><span class="line"><span class="javascript">            vm.product = <span class="string">&#x27;我改变了&#x27;</span></span></span><br><span class="line"><span class="javascript">            vm.list = <span class="string">&#x27;你好&#x27;</span></span></span><br><span class="line"><span class="javascript">            <span class="built_in">console</span>.log(vm.$options.el.innerHTML,<span class="string">&#x27;---&#x27;</span>)</span></span><br><span class="line">        &#125;,1000)</span><br><span class="line">    <span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 我们打印出来可以看到 拿到的还是之前的DOM元素</span><br><span class="line"><span class="number">2.</span> 这里我们可以看到 我们的DOM元素 数据已经由<span class="number">333</span> 变成你好了 但是这里我们拿到的html还是原来的</span><br></pre></td></tr></table></figure>
<p><img src="2.gif" alt=""></p>
<h2 id="nextTick方法"><a href="#nextTick方法" class="headerlink" title="$nextTick方法"></a>$nextTick方法</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 所以这里我们就要采用这种$nextTick 去拿到最新的DOM</span><br><span class="line"><span class="number">2.</span> 为什么这么做 因为你视图更新是异步的 当我们同步代码执行完步之后 你的视图还没更新过来</span><br><span class="line"><span class="number">3.</span> 这里我们的核心思想就是 把你的视图更新的代码 变成微任务 然后排在任务队列的第一位 所有需要视图更新拿到的结果 都一次向后排列执行</span><br><span class="line"><span class="number">4.</span> 这样就能保证我们拿到最新的渲染后的DOM了</span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 所以我们刚刚的异步更新是采用定时器的方法 定时器是宏任务 这里我们采用promise的方法</span><br><span class="line"><span class="number">2.</span> 这里就要单写一个nextTick文件了</span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// observe / schedular.js</span></span><br><span class="line"><span class="keyword">import</span> &#123; nextTick &#125; <span class="keyword">from</span> <span class="string">&quot;../util&quot;</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> has = &#123;&#125;</span><br><span class="line"><span class="keyword">let</span> queue = []</span><br><span class="line"><span class="keyword">let</span> pending = <span class="literal">false</span></span><br><span class="line"><span class="keyword">export</span> <span class="function"><span class="keyword">function</span> <span class="title">queueWatcher</span>(<span class="params">watcher</span>)</span>&#123;</span><br><span class="line">    <span class="keyword">let</span> id = watcher.id</span><br><span class="line">    <span class="keyword">if</span>(has[id] == <span class="literal">null</span>)&#123;</span><br><span class="line">        queue.push(watcher)</span><br><span class="line">        has[id] = <span class="literal">true</span></span><br><span class="line"></span><br><span class="line">			 <span class="comment">// pending 主要是为了防止不同watcher 创建多个 微任务</span></span><br><span class="line">       <span class="keyword">if</span>(!pending)&#123;</span><br><span class="line">           pending = <span class="literal">true</span></span><br><span class="line">        	 nextTick(flushSchedularQueue)</span><br><span class="line">       &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">flushSchedularQueue</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">&#x27;执行一次&#x27;</span>)</span><br><span class="line">    <span class="keyword">for</span>(<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; queue.length; i++)&#123;</span><br><span class="line">        <span class="keyword">let</span> watcher = queue[i]</span><br><span class="line">        watcher.run()</span><br><span class="line">    &#125;</span><br><span class="line">    queue = []</span><br><span class="line">    has = &#123;&#125;</span><br><span class="line">    pending = <span class="literal">false</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 2021 0218</span></span><br><span class="line"><span class="keyword">let</span> callbacks = []</span><br><span class="line"><span class="keyword">let</span> waiting = <span class="literal">false</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">flushCallbacks</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="keyword">for</span>(<span class="keyword">let</span> i = <span class="number">0</span>; i&lt;callbacks.length;i++)&#123;</span><br><span class="line">        <span class="keyword">let</span> callback = callbacks[i]</span><br><span class="line">        callback()</span><br><span class="line">    &#125;</span><br><span class="line">    waiting = <span class="literal">false</span></span><br><span class="line">    callbacks = []</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">//1. 这里我们视图更新的时候会调用这个函数 cb就是我们视图更新的函数</span></span><br><span class="line"><span class="keyword">export</span> <span class="function"><span class="keyword">function</span> <span class="title">nextTick</span>(<span class="params">cb</span>)</span>&#123;</span><br><span class="line">    <span class="comment">// 我们向数组里存放这个视图更新的函数</span></span><br><span class="line">    callbacks.push(cb)</span><br><span class="line">    <span class="keyword">if</span>(!waiting)&#123;</span><br><span class="line">    <span class="comment">// 第一次我们进入到这个if里来    然后改变锁</span></span><br><span class="line">        waiting = <span class="literal">true</span></span><br><span class="line">        <span class="comment">//这个时候 我们的then后面的函数 会被放到微任务里来 等到同步代码执行完毕之后才会执行</span></span><br><span class="line">        <span class="comment">// 我们的同步代码还有 vm.$nextTick(() =&gt; &#123; console.log(vm.$options.el.innerHTML,&#x27;---&#x27;)&#125;)没有执行</span></span><br><span class="line">        <span class="comment">// 所以再次调用 nextTick这个函数 于是就会在向callbacks 里去存放我们的回调函数 函数是 打印的这个函数</span></span><br><span class="line">        <span class="comment">// 然后 没有同步代码了 我们开始执行微任务里的函数 callbacks 数组里有两个函数 一个是 更新视图的函数 一个是 获取最新DOM的函数</span></span><br><span class="line">        <span class="comment">// 然后一次执行 所以DOM更新完了 然后执行打印拿到最新DOM的函数 </span></span><br><span class="line">        <span class="comment">// 这就是 $nextTick的原理 多个任务执行 只开启一个微任务</span></span><br><span class="line">        <span class="built_in">Promise</span>.resolve().then(flushCallbacks)</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 首先我们知道 我们每改变一次 data中的数据的时候 就会调用watcher中一次更新的方法 就会重新渲染页面</span><br><span class="line"><span class="number">2.</span> 所以我们改变数据的时候 只调用一次 watcher中的更新方法 并且 我们只取最后一次改变值的 更新方法 而且是异步的去更新</span><br><span class="line"><span class="number">3.</span> 首先我们改变数据的时候 我们要保证 数据对应的dep里的watcher 要去重</span><br><span class="line"><span class="number">4.</span> 然后我们写一个nextTick方法 把我们更新的方法传入进去 然后我们开启一个promise 把更新的视图的方法也就是watcher中的方法 存放进去 </span><br><span class="line"><span class="number">5.</span> 这样当我们 同步代码 都执行完毕了之后 就会去执行微任务中的代码 也就是watcher中更新视图的函数 </span><br><span class="line"><span class="number">6.</span> 然后 当我们需要拿到最新DOM的时候 我们再次调用 nextTick 把需要执行的代码 放入到我们的 我们微任务中的队列去 也就是放入到了我们的 watcher中更新函数的后面 </span><br><span class="line"><span class="number">7.</span> 等到同步代码执行完毕之后 我们就一次循环这个队列 然后一次执行 这个时候代码是同步</span><br><span class="line"><span class="number">8.</span> 我们就能保证 每次视图先更新 然后 再去执行我们的逻辑代码 拿到最新的数据</span><br></pre></td></tr></table></figure>
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<p style="background:rgba(255,255,255,1);margin:0"> <img src="/img/code.png"></img> </p></div></div><div class="sticky_layout"><div class="card-widget" id="card-toc"><div class="item-headline"><i class="fas fa-stream"></i><span>目录</span></div><div class="toc-content"><ol class="toc"><li class="toc-item toc-level-1"><a class="toc-link" href="#Vue%E6%BA%90%E7%A0%81%E5%BC%80%E5%8F%91-%E6%89%B9%E9%87%8F%E6%9B%B4%E6%96%B0"><span class="toc-text">Vue源码开发-批量更新</span></a><ol class="toc-child"><li class="toc-item toc-level-2"><a class="toc-link" href="#%E5%BC%82%E6%AD%A5%E6%9B%B4%E6%96%B0-%E6%89%B9%E9%87%8F%E6%9B%B4%E6%96%B0"><span class="toc-text">异步更新 批量更新</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#%E5%AD%98%E5%9C%A8%E9%97%AE%E9%A2%98"><span class="toc-text">存在问题</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#nextTick%E6%96%B9%E6%B3%95"><span class="toc-text">$nextTick方法</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#%E6%80%BB%E7%BB%93"><span class="toc-text">总结</span></a></li></ol></li></ol></div></div><div class="card-widget card-recent-post"><div class="item-headline"><i class="fas fa-history"></i><span>最新文章</span></div><div class="aside-list"><div class="aside-list-item"><a class="thumbnail" href="/2021/04/16/gin-vue-admin/" title="Gin-Vue-Admin"><img src="/img/gin-vue-admin.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Gin-Vue-Admin"/></a><div class="content"><a class="title" href="/2021/04/16/gin-vue-admin/" title="Gin-Vue-Admin">Gin-Vue-Admin</a><time datetime="2021-04-15T16:00:00.000Z" title="发表于 2021-04-16 00:00:00">2021-04-16</time></div></div><div class="aside-list-item"><a class="thumbnail" href="/2021/01/08/Vue%E6%BA%90%E7%A0%81%E5%BC%80%E5%8F%91%E4%B9%8B%E7%BB%84%E4%BB%B6%E7%9A%84%E6%B8%B2%E6%9F%9310/" title="Vue源码开发-组件的渲染10"><img 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